Alkyl propionates are of interest as solvents, as flavorings and as perfumes. They may be prepared by reacting an alkanol in the liquid phase with ethene and carbon monoxide in a reaction vessel in the presence of a carbonylation catalyst, for example as described in European Patent Application Nos. 0106379, 0235864 and 0279477.
The components of carbonylation catalysts are expensive, and so it is important to minimize the amounts of components consumed per tonne of alkyl propionate produced. Thus, the continuous process described in European Patent Application No. A-0279477 involves a step in which catalyst removed from the reaction vessel during recovery of alkyl propionate is recycled back to the reaction vessel.
The continuous process described in European Patent Application No. 0279477 is relatively complex and, in spite of the catalyst recycle step, consumes relatively large amounts of catalyst components per ton of alkyl propionate produced.
It has now been found that alkyl propionates may be prepared by a carbonylation process in which the amounts of catalyst components consumed are relatively small.